充分和通风盘式制动器的车辆的热行为111副本.doc

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1、【精品文档】如有侵权，请联系网站删除，仅供学习与交流充分和通风盘式制动器的车辆的热行为111副本.精品文档. 附录A外文翻译-原文部分Journal of Mechanical Science and Technology 26 (11) (2012) 36433652 DOI 10.1007/s12206-012-0840-6 Thermal behavior of full and ventilated disc brakes of vehicles A. Belhocine* and M. Bouchetara Faculty of Mechanical Engineering, Uni

2、versity of Sciences and the Technology of Oran, L.P 1505 El -MNAOUER, USTO 31000, Oran, Algeria (Manuscript Received January 23, 2011; Revised June 23, 2012; Accepted June 28, 2012) Abstract Braking is a process which converts a vehicles kinetic energy into mechanical energy which must be dissipated

3、 in the form of heat. During the braking phase, the frictional heat generated at the interface of the disc and pads can lead to high temperatures. This phenome-non is even more important than the tangential stress. The relative sliding speeds during contact are also important. The prediction of surf

4、ace temperature for a brake rotor is regarded as an important step in studying brake system performance. The frictional heat generated on the rotor surface can influence excessive temperature rise which, in turn, leads to undesirable effects such as thermal elastic instability (TEI), premature wear,

5、 brake fluid vaporization (BFV) and thermally excited vibrations (TEV). The objective of this study is to analyze the thermal behavior of the full and ventilated brake discs of the vehicles using computing code ANSYS. The modeling of the tempera-ture distribution in the disc brake is used to identif

6、y all the factors and the entering parameters concerned at the time of the braking opera-tion, such as the type of braking, the geometric design of the disc and the material used. The results obtained by the simulation are satis-factory compared to those of the specialized literature. Keywords: Fric

7、tion; Brake discs; Transient mode; Heat flux; Heat transfer coefficient1. IntroductionThermal analysis is a primordial stage in the study of brake systems, because the temperature determines the structures thermomechanical behavior. In the braking phase, tempera-tures and thermal gradients are very

8、high. This generates stresses and deformations whose consequences are manifested by the appearance and the accentuation of cracks 1, 2. It is then important to precisely determine the temperature field of the brake disc. The ventilated discs used in the brake system of automobiles require rapid cool

9、ing performance and robust structural design to prevent thermal deformation since their temperature increases greatly during braking. A disc with good cooling performance can control its temperature rise and prevent thermal-related problems such as hot judder, which is caused by the thermal de-forma

10、tion of the disc, rapid wearing of the pad and vapor lock of the brake oil caused by heat transfer to the caliper 3. Therefore, in the early design stage, the temperature increase and thermal performance of a disc need to be predictable. The thermal characteristics of a disc have been estimated and

11、analyzed in many studies. Faramarz 4 extracted the governing equations for heat transfer on a*Corresponding author. Tel.: +213793851317E-mail address: al.belhocineyahoo.fr Recommended by Associate Editor Vikas Tomar?KSME & Springer 2012simple disc and pad assembly and solved the equations usingGreen

12、s function. Faramarz calculated the temperature rise of the disc by assuming that all of the kinetic energy of a vehicle was converted into thermal energy. Kim 5 investigated the effects of design parameters for a ventilated disc on the tem-perature distribution of the disc surface by using a three-

13、dimensional unsteady model created by FLUENT.Choi 6 compared the thermal dissipation performance of two discs: one had normal vents and the other had helical grooved vents. Choi used a finite element analysis technique and simulated a piece of the disc under the repeated braking mode. Kim 7 proposed

14、 the analysis method using FE soft-ware (ANSYS) to predict the temperature distribution and thermal deformation of a disc.Hwang 8 conducted a thermo-mechanical coupling analy-sis of a partial three-dimensional disc brake model and dis-cussed the temperature and contact pressure distributions of a di

15、sc. These studies insufficiently predict the temperature rise of a disc because the vehicle and brake information and the mechanical characteristics of the hydraulic components of the brake system are not considered. Most studies assumed that one-fourth of the kinetic energy of a vehicle was fully c

16、hanged into thermal energy under ideal braking circumstances and calculated the heat flux to be applied to the disc brake module 9. Thus, the change in the mechanical energy of a vehicle according to the performance of its hydraulic brake system East China Jiaotong University (218.65.102.178) - 2013

17、/4/12 Download3644A. Belhocine and M. Bouchetara / Journal of Mechanical Science and Technology 26 (11) (2012) 36433652and braking condition could not be considered in the simula-tion model.In 2002, Nakatsuji et al. 10 did a study on the initiation of hair-like cracks that formed around small holes

18、in the flange of one-piece discs during overloading conditions. The study showed that thermally induced cyclic stress strongly affects crack initiation in the brake discs. In order to show the crack initiation mechanism, the temperature distribution at theTable 1. Geometrical Dimensions and applicat

19、ion parameters of auto-motive braking.Vehicle mass- m kg1385Initial speed - v0 km/h28Deceleration -a m/s28Effective rotor radius-R rotor mm100.5Rate distribution of the braking forces- - %20Factor of charge distribution on the disc 0.5flange had to be measured.Using the finite element method, the te

20、mperature distribu-tion under overloading was analyzed. 3D unsteady heat trans-fer analyses were conducted using ANSYS. A 1/8 section of the one-piece disc was divided into finite elements, and the model had a half thickness due to symmetry in the thickness direction. The disc rotates 6 times during

21、 one braking, which means it is heated up and cooled down 6 times in one braking. Therefore, each braking was divided into 13 periods, includ-ing an idling period of 30 seconds.In 2000, Valvano and Lee 11 did a study on the technique to determine the thermal distortion of a brake rotor. The se-vere

22、thermal distortion of a brake rotor can affect importantpSurface disc swept by the pad Ad mm235993Table 2. Thermophysical properties of the disc 16.Thermophysical properties of the discValuesYoung modulus E (MPa)138000Poisson coefficient 0.28Density (kg/m3)7250Thermal expansion (1/癈)1.085 ?10-5Tensi

23、le strength (MPa)300Compressive strength (MPa)820 brake system characteristics, such as the system response and brake judder propensity. As such, the accurate prediction of thermal distortions can help in the designing of a brake disc. In 1997, Hudson and Ruhl 12 did a study on air flow through the

24、passage of a Chrysler LH platform ventilated brake rotor. Modifications to the production rotors vent inlet geometry were prototyped and measured in addition to the production rotor. Vent passage air flow was compared to ex-isting correlations. With the aid of Chrysler Corporation, in-vestigation of

25、 ventilated brake rotor vane air flow was under-taken. The goal was to measure current vane air flow and to improve this vane flow to increase brake disc cooling. In 2009, Hwang and Wu 13 investigated the temperature and thermal stress in the ventilated disc-pad brake during sin-gle brake based on m

26、ulti-body technique and 3D thermome-chanical coupling model.In this study, we will present a numerical modeling in three dimensions to analyze the thermal behavior of the full and ventilated disc brake.The thermal calculation based on the finite element method will be carried out using ANSYS 11 code

27、.Fig. 1. Disc-pads assembly with forces applied to the disc.brake disc. The heat flux evacuated from this surface is equal to the friction power. The initial heat flux q 0 entering the discis calculated by the following formula 14:1 mgv 0 z2. Heat flux entering the discIn a braking system, mechanica

28、l energy is transformed into calorific energy. This energy is characterized by a total heat-ing of the disc and pads during the braking phase. The energy dissipated in the form of heat can generate temperature in-creases ranging from 300癈 to 800癈. The heat quantity in the contact area is the result

29、of plastic micro-deformations gener-ated by the friction forces.Generally, the thermal conductivity of the brake pad mate-rial is lower than that of the disc k p kd We consider thatthe heat quantity produced will be completely absorbed by theq 0 =,(1)22 A d pwhere z = a / g is braking effectiveness.

30、Fig. 1 shows the ventilated disc-pads and the applied forces. The loading corresponds to the heat flux on the disc surface. The dimensions and the parameters used in the thermal calcu-lation are recapitulated in Table 1.The disc material is gray cast iron with high carbon content FG, with good therm

31、ophysical characteristics which are given in Table 2 15. The thermal conductivity and specific heat are a function of temperature 16, Figs. 2 and 3. East China Jiaotong University (218.65.102.178) - 2013/4/12 DownloadA. Belhocine and M. Bouchetara / Journal of Mechanical Science and Technology 26 (1

32、1) (2012) 364336523645C Fig. 2. Thermal conductivity versus temperature. Fig. 4. Simulation steps with CFX 17. tem of equations of finite dimension, which we can schematically write in the form AU = L, where U is the vector of the unknowns, A is a matrix and L is a vector.CFig. 3. Specific heat vers

33、us temperature.3. Presentation of the computing code ANSYSThe modules used for this study are:4.2 Equation of the problemThe first law of thermodynamics indicating the thermal conservation of energy gives: T ANSYS Workbench: This platform offers a different ap-proach in the construction of a model u

34、sing the original com-puter code ANSYS 17. It is particularly adapted to handling cases with complex geometries and unconfirmed users. In this environment, the user works on the geometry and not on the model itself. Before starting the solution, the platform will C p + vTL T + L T Q = p(2) tIn our c

35、ase, there is not an internal source, and thus, Eq. (2) is written as follows: Tconvert the data introduced by the user into code ANSYS. Thegenerated finite element model is handled by inserting specific commands of ANSYS code. ANSYS ICEM CFD: Mesh generation software for appli-cations in fluid mech

36、anics and mechanical structures. ANSYS CFX: This software is designed to perform simu-lations in fluid mechanics. ANSYS Metaphysics: This product contains all modules C p with+vTL T + L T Q = 0(3) t x of ANSYS simulation code.Fig. 4 shows the stages of simulation with ANSYS CFX in Workbench.L = (4)

37、y z 4. Numerical modeling of the thermal problemvxv= v(5)4.1 Finite element methodyThe finite element method is used in many applications tosolve partial differential equations 18. It leads to a simple approximation of the unknown factors of continuous equa-tions. These approximations are then trans

38、formed into a sys- vz Fouriers law (3) can be written in the following matrix form: East China Jiaotong University (218.65.102.178) - 2013/4/12 Download3646 Q with kA. Belhocine and M. Bouchetara / Journal of Mechanical Science and Technology 26 (11) (2012) 36433652K L T(6)xx00 K k ,k= 0k yy0 (7) 00

39、k zz and kRepresent the thermal conductivity along axes xyzx, y, z, respectively. In our case, the material is isotropic, andthus k xx = k yy = kzz L Vector operator. v Vector speed of mass transport. K Conductivity matrix.By combining Eqs. (3) and (6), we obtain: TFig. 5. Brake disc CFD model.the b

40、rake lining.C p + vTL T t + L T ( K L T )(8)When a vehicle brakes, a part of the frictional heat escapes to the ambient air by convection and radiation. Consequently,By developing Eq. (8), we obtain: T T T T the determination of the heat transfer coefficients is essential.Their exact calculation is,

41、 however, rather difficult, because these coefficients depend on the location and the construction C+ v+ v+ vof the braking system, the speed of the travelling vehicle and,p xyz t x y z T T T (9)consequently, air circulation. Since the process of heat transfer by radiation is not significant, we wil

42、l only determine the con- x k x + k y + k z x y y z z vection coefficient (h) of the disc using code ANSYS CFX. This parameter will be exploited to determine the three-4.3 Initial conditionsWe suppose that the initial temperature of the disc is con-stant.odimensional distribution of the temperature

43、of the disc.5.1 Modeling in ANSYS CFXThe first stage is to create the CFD model which contains the fields to be studied in Ansys Workbench. In our case, weT ( x, y, z, t) = 60 Cat time t = 0(10)4.4 Boundary conditionsThis is a transient thermal problem with two boundary con-ditions:A heat flux enter

44、ing the disc localized in the contact zone disc-pad on both sides.A heat transfer by convection on all the free surfaces of the disc of which the exchange coefficient h depends on time because rotational speed of the disc varies with time.The heat transfer coefficient, h, on each disc surface was ca

45、lculated and imported using ANSYS CFX module.5. Determination of the heat transfer coefficient by convection (h)The thermal analysis of the braking system requires a pre-cise determination of the quantity of heat friction produced as well as the distribution of this energy between the disc and the b

46、rake lining. During emergency braking, all the heat produced at the interface is equal to the heat absorbed by the disc andtook only one quarter of the disc, then we defined the field ofthe air surrounding this disc. ANSYS ICEM CFD prepared various surfaces for the two fields in order to facilitate the mesh on which it will export the results to CFX using the command Output to cfx. After obtaining the model on CFX Pre and specifying the boundary conditions, we mu